GIS and Frequency Analysis for the Identification of Vulnerable Areas to Extreme Hydrological Events

The extreme hydrological events to which we refer in this study are water excess and drought, and the analyzed territory is Transylvania. The study does not use two types of magnitudes for the representation of water excess and drought, respectively. Based on the VUB model of the monthly precipitation-runoff relation (Vandewiele et al. 1993), the monthly series of the basin water reserve is calculated, series equivalent to the basin mois-ture index. The time series of the basin moisture index is submitted to frequency analysis in order to obtain a probabilistic expression of the extremes. The maximum extremes of the simulated population will reflect different water excess categories, and the minimum ex-tremes of the simulated population will reflect different drought categories. By a regression analysis, the influence of relief on the spatial variation of the basin moisture index is calcu-lated. The regression equations obtained for various probabilities are transferred to ArcGIS, and maps of the vulnerability of extreme hydrological events are obtained, the unit of measure being the return period of water excess or drought.